Tải bản đầy đủ - 0 (trang)
Th. ponticum Partial Amphiploid OK7211542

Th. ponticum Partial Amphiploid OK7211542

Tải bản đầy đủ - 0trang

Genetic Diversity for Wheat Improvement as a Conduit to Food Security



225



Sr38 (Aegilops ventricosa). The recent appearance of pathotypes of Ug99 stem

rust (Pretorius et al., 2000, 2010), which has overcome the Sr31 gene on

that 1RS chromosome as well as about 26 other stem rust resistance genes

(Jin et al., 2007; Pretorius et al., 2010), highlights the need to continually

search for, identify, and transfer new disease resistance genes into

wheat cultivars.

The question arises as to what research scientists should do when

urgently seeking resistance genes to a new disease or an aggressive, virulent

pathotype of an existing disease that has emerged? The simple answer is that

there is no realistic alternative than to use resistance genes occurring in

nature. There is no stash of novel, effective, cloned resistance genes stored

in freezers in laboratories around the World that can be thawed and then

deployed quickly in farmers’ fields to avert potential crisis that may threaten

food security in developing countries as reflected in the Ug99 incidence.

Some fundamental principles emerge:

a. There is no shortage of disease resistance genes in wild uncultivated or

distantly related species to wheat. It is logical and responsible to pursue

and utilize this valuable resource.

b. There is no relationship between the ease or difficulty of crossing or

inducing chromosome pairing with wheat and the durability of the

resistance genes. In other words, the most distantly related genera/species to wheat do not necessarily contain the most effective or longlasting resistance genes. An example of this is Sr31 from rye, which

eventually succumbed to virulent stem rust pathotype TTKSK after

many decades of use in agriculture. The main advantage of turning

to wild or distantly related species is that resistance genes are readily

found in wild relatives.

c. Success in wide crossing or chromosome engineering cannot be

predicted beforehand. For this reason, it is wise to maximize the

chances of success by diversifying and attempting hybridization and

alien chromosome transfers with a range of species, accessions, or

landraces simultaneously.

There are two principal factors governing the use of wild species as a source

of agriculturally important characters, namely, (a) obtaining a fertile hybrid

and (b) successfully transferring the chromosome segment carrying resistance

to a wheat chromosome. Successful hybridization, survival of the F1, and

recovery of viable recombinants may be influenced by chance genetic factors

as well as chromosome structural heterozygosity. Not all crosses between

accessions of T. dicoccoides or Ae. speltoides and wheat are successful



226



A. Mujeeb-Kazi et al.



(I. Dundas, unpublished data). Species with genomes closely related to

wheat (e.g., A, B, and D genomes) usually demonstrate high rates of recombination with wheat. More distantly related species to wheat usually

show reduced rates of homoeologous pairing. Recombinants between

“S” genome chromosomes (Ae. speltoides) and wheat (principally the

B genome) have been readily obtained (see above chromosomes 2S#1

and 2S#2). Th. ponticum and Th. intermedium chromosomes also recombine

with wheat, however, at a lower but still recoverable rate (see above chromosomes 6Ae#1 and 7Ai#1). Great difficulty has been experienced in producing some wheat–rye recombinants (see above chromosomes 5R and

6R), with the exception of chromosome 1R, which has the least degree

of structural rearrangements of any of the “R” genome chromosomes

(Devos et al., 1993). If the pairing chromosomes differ in the structural

arrangement of chromosome segments, so that homologous sections cannot

align to form chiasmata or where crossover products are sterile, then recovery of homologous or homoeologous recombinants with wheat will always

present a problem, irrespective of the taxonomic relationships.

Further contributions from Secale (6RL) for powdery mildew resistance

locus (Wang et al., 2010a,b) and from Rogeneria ciliaris (Wang et al., 2001) are

reported resources. Some new translocations have been identified (mentioned in Table 4.3) that are removed from practical usage in active breeding

programs but have enhancing wheat productivity impact potential.

Majority of the earlier produced translocations have been predominantly

in genetic backgrounds that prevent their global exploitation readily as the

wheat cultivar involved was not widely adapted. Thus, very few are in practical use. This led to the need of having these valued stocks transferred into

good agronomic wheat backgrounds of some varieties of Pakistan. The

translocations utilized for an initial transfer process have been T1AL.1RS

(Fig. 4.9), T1BL.1RS (Fig. 4.4), T4BS.4BL-2R (Fig. 4.10), T7DS.7DL7Ag (Fig. 4.11), T2BS.2RL (Fig. 4.12), T4BS.4BL-5RL (Fig. 4.13),

T6BS.6RL (Fig. 4.14), and T2AS-2RS.2RL (Fig. 4.15). Using the reciprocal backcrossing protocol around varietal choice of “INQUILAB91,”

PAK-81, and “TD-1,” the above translocations have been made

user friendly.

Additive to the above data are contributions focused on wheat/alien

chromosome translocations from some research programs of USA, China,

and Japan that address pest resistance, abiotic stresses, and crop management

production essentials.



227



Genetic Diversity for Wheat Improvement as a Conduit to Food Security



Table 4.3 New translocations with practicality potential relative to biotic stress

resistances important for enhancing wheat productivity

Translocation

Targeted trait

Alien species

Reference



T5DS.5DL-5MgL-5 Sr53

DL



Ae. geniculata



Liu et al. (2011)



T5DS.5DL-5MgL-5 Sr53

MgS



Ae. geniculata



Liu et al. (2011)



T6AS.6V # 3L



Sr52



D. villosum



Qi et al. (2011)



T7DS.5Lr



Scab



L. racemosus



LinSheng et al.

(2010)



T6VS.6AL



Powdery mildew D. villosum



T1BS.1BL-4AgL



Blue grain



Th. ponticum



Zheng et al. (2006)



T2DL.4AgL



Blue grain



Th. ponticum



Zheng et al. (2006)



T4AgL.3AL



Blue grain



Th. ponticum



Zheng et al. (2006)



T4AgL.4AL



Blue grain



Th. ponticum



Zheng et al. (2006)



T5BS.5BL-4AgL



Blue grain



Th. ponticum



Zheng et al. (2006)



T6DL.$Agl



Blue grain



Th. ponticum



Zheng et al. (2006)



T6BL.6BS-4AgL



Blue grain



Th. ponticum



Zheng et al. (2006)



T7AL.7AS-4AgL



Blue grain



Th. ponticum



Zheng et al. (2006)



T7DS.7DL-7EL



Bdv3



Th. intermedium



Kong et al., 2009



T4VS.4DL



Wheat spindle

streak virus



H. villosa



Zhang et al. (2005)



T2BL.1RS



Yr and mildew



Secale



Wang et al.

(2009a,b)



T1RS.1VL



Academic



Rye/D.villosum



Ksiazczyk et al.

(2011)



T7DL.7Ag



Physiological



L. elongatum



Monneveux et al.

(2003)



T1DS.1V # 3L



Quality



D. villosum



Zhao et al. (2010)



T1DS.1V # 3S



Quality



D. villosum



Zhao et al. (2010)



T4BS.4BL-5RL



Cu. Efficiency



Secale



Leach et al. (2006)



T2BS.2RL



Multiple stress



Secale



Hysing et al. (2007)



Various reviewed



Multiple stress



Various



Wang (2011)



Li et al. (2007)



228



A. Mujeeb-Kazi et al.



Figure 4.9 The T1AL.1RS Robertsonian translocation (heterozygote) in bread wheat.



Figure 4.10 The T4BS.4BL-2R translocation in bread wheat.



Figure 4.11 The T7DS.7 DL.7Ag translocation in bread wheat.



Genetic Diversity for Wheat Improvement as a Conduit to Food Security



Figure 4.12 The T2BS.2RL translocation in bread wheat.



Figure 4.13 The T4BS.4BL-5RL translocation in bread wheat.



Figure 4.14 The T6BS.6RL translocation in bread wheat.



229



230



A. Mujeeb-Kazi et al.



Figure 4.15 The T2AS-2RS.2RL translocation in bread wheat.



10.1. Pest/biotic stress resistance

Anderson et al. (2010) tested 19 Chinese Spring  L. elongatum (syn.

Thinopyrum elongatum) disomic substitution lines for resistance to barley yellow dwarf virus (BYDV), cereal yellow dwarf virus (CYDV), Hessian fly

Mayetiola destructor, and the fungal pathogens Blumeria graminis and

Mycosphaerella graminicola (asexual stage: Septoria tritici). They reconfirmed

that genes on more than one Lophopyrum chromosome are required for complete resistance to BYDV. A potentially new gene for resistance to CYDV

was detected on wheatgrass chromosome 3E. All of the substitution lines

were susceptible to M. destructor and one strain of B. graminis. Disomic substitution lines containing 1E and 6E were significantly more resistant to

M. graminicola compared to Chinese Spring but neither chromosome by itself

conferred resistance as high as that in the wheatgrass parent.

The above stocks allow for engineering wheat/alien translocation events

in the future. This is particularly important since resistance diversity is rather

minimal conventionally.

In his most recent review, Wang (2011) concluded that Th. intermedium

and Th. ponticum had been the two most valuable wild relatives

contributing a wide range of desirable traits to wheat cultivar development.

It is because that these two species contain the basic genomes E- (or J-) and

St that are closely related to A and D genomes of bread wheat. Only recently,

chromosome arm or segment(s) of more distantly related genomes have been

translocated onto wheat chromosomes. Stripe rust resistance on a small

terminal segment from the short arm of 3Ns chromosome in

Psathyrostachys huashanica was translocated to the terminal region of wheat



Genetic Diversity for Wheat Improvement as a Conduit to Food Security



231



chromosomes 3BL in the wheat line PW11-8 (Kang et al., 2011). The

translocation was designated by the authors as T3BL-3NsS, but it

appeared to be T3BLÁ3BS-3NsS. Two 3Ns-specific SSR markers,

Xgwm181 and Xgwm161, were found useful to rapidly identify and trace

the translocated fragments.

Li and Wang (2009) listed genes for fungal and viral disease resistance

derived from Th. ponticum and Th. intermedium. They warned about the

threat of new races of stem rust Ug99 that could overcome the protection

provided by existing Sr genes. Fortunately, the disomic T. aestivum–

Th. junceum addition line H3505 was moderately resistant to the stem rust

Ug99 races (Xu et al., 2009). Two disomic T. aestivum–Elymus rectisetus

addition lines (A1026 and A1034) and three disomic T. aestivum–

Th. junceum addition lines (AJDAj2, AJDAj3, and AJDAj6) exhibited

resistance to Fusarium head blight (FHB) or scab (McArthur et al., 2012).

Disomic addition lines A1057 was moderately resistant to both tan spot

and SNB and its resistance levels to both diseases were significantly higher

than its wheat parent Fukuho-komugi (Oliver et al., 2008). A1026 and

A1057 carry the 1St and 1Y chromosome, respectively (Dou et al.,

2012), whereas A1034 contains a Group-5 E. rectisetus chromosome

(McArthur et al., 2012). AJDAj2, AJDAj3, AJDAj6, and H3505 contain

2E, 2E, (2E ỵ 5E), and 4E chromosomes, respectively, of Th. junceum

(Wang et al., 2010a,b). Both Wang et al. (2010a,b) and McArthur et al.

(2012) suggested that the 2E in AJDAj2 and AJDAj3 were probably originated from the two Eb (¼J) genomes of Th. junceum, which has the genome

composition Eb1 Eb2 Ee (¼J1J2E). Similarly, the 1E in AJDAj7 and AJDAj9

also originated from the Eb genome. Thus, the 2E in AJDAj4 and 1E in

AJDAj8 belonged to the Ee genome. The above are still far removed from

practical breeding usage but are potent resources from which cytogenetic

manipulations could generate translocation events of benefit and expand

the allelic diversity available for wheat breeding.



10.2. Abiotic stress tolerance

The chromosome carrying salt tolerance gene in AJDAj5 has been determined to be a (1E ỵ 5E) recombined chromosome based on EST-SSR

markers (Wang et al., 2010a,b). The salt tolerance of AJDAj5, along with

that of the PhI line, has been transferred to wheat in the two translocation

lines W4909 and W4910 (Mott and Wang, 2007; Wang et al., 2003a,b).

Because W4909 and W4910, the PhI line, could tolerate high sodium concentrations in the shoots (Genc et al., 2007; Mott and Wang, 2007), the gene



232



A. Mujeeb-Kazi et al.



for tissue tolerance to salinity must have been contributed from Ae. speltoides

when the PhI gene was transferred into Chinese Spring wheat. W4909 and

W4910 are also drought tolerant, because a small decrease in total proteins

and Rubisco was noted in W4909 and W4910, while a significantly higher

reduction was recorded in control cultivar Yecora Rojo (Bhutto, 2010).



11. SOME ONGOING STUDIES AND THE WAY

FORWARD STRATEGY WITH ALIEN RESOURCES

11.1. Translocations from Leymus racemosus and

H. vulgare

Kishii et al. (2004) produced a number of Robertosonian translocations

between wheat and L. racemosus chromosomes by crossing wheat monosomic

lines (Table 4.4) and later on also developed EST linkage map (Larson et al.,

2012). The breakpoints of all of these lines were confirmed at centromeric

regions by GISH. Even though phenotypic evaluations have not been conducted in detail for the translocation lines, preliminary screenings of their

parental addition lines revealed that L. racemosus chromosome 7Lr#2 (¼Lr#J),

5Lr#2 (¼Lr#I), 3Lr#4 (¼Lr#N) possessed the “Biological Nitrification Inhibition” character that would prevent emission of N2O global warming gas

from nitrogen fertilizer usage during cultivation (Subbarao et al., 2007).

The addition lines 2Lr#3 (¼Lr#L) and 7Lr#2 (¼Lr#J) also possessed novel

leaf rust and stem rust resistance genes (Kishii et al., 2004; unpublished data).

Because the homoeology between wheat and L. racemosus chromosomes is

partially conserved (Kishii et al., 2004; Qi et al., 1997), the translocation events

are anticipated to be partially compensating in most cases.

Taketa et al. (2005) produced barley translocation lines of 5H chromosome by inducing homoeologous recombination from H. vulgare cv. New

Golden using the ph1 mutant line and nullitetrasomic line. Five translocations were recovered as either T5DS-5DL.5H#2L or T5DL-5DS.5H#2S, with

one being an intercalary translocation—T5DS-5DL.5H#2L-5DL. The length

of the translocated segments was well characterized by STS markers. Phenotypical characters of the translocations have yet to be published.



11.2. Production of new translocations

Wheat/alien chromosome translocations attract enormous attention and this

is due to the practical benefits that are seen globally from the T1BL.1RS

spontaneous event. The transfer from winter wheat to spring habit cultivars

added further to interest. Seeing this promise the standard route of



233



Genetic Diversity for Wheat Improvement as a Conduit to Food Security



Table 4.4 Translocations involving wheat and Hordeum and Leymus species

Alien

Germplasm species

Description

Mode of transfer

References



Line #112



H. vulgare



T5DS5DL.5HL-5DL



Homoeologous

recombination



Taketa

et al. (2005)



Line #489



H. vulgare



T5DS-5DL.5HL



Homoeologous

recombination



Taketa

et al. (2005)



Line #702



H. vulgare



T5DS-5DL.5HL



Homoeologous

recombination



Taketa

et al. (2005)



Line #170



H. vulgare



T5DL-5HL.5HS



Homoeologous

recombination



Taketa

et al. (2005)



Line #171



H. vulgare



T5DL-5HL.5HS



Homoeologous

recombination



Taketa

et al. (2005)



Line #546



H. vulgare



T5DL-5HL.5HS



Homoeologous

recombination



Taketa

et al. (2005)



3BL/

Lr#HS



L. racemosus



T3BL/3Lr#2S

(Lr#H)



Homoeologous

Robertsonian



Kishii

(2011)



3BS/

Lr#HS



L. racemosus



T3BS/3Lr#2L

(Lr#H)



Homoeologous

Robertsonian



Kishii

(2011)



5BL/

Lr#IS



L. racemosus



T5BL/5Lr#2S

(Lr#I)



Homoeologous

Robertsonian



Kishii

(2011)



5BS/

Lr#IL



L. racemosus



T5BS/5Lr#2L

(Lr#I)



Homoeologous

Robertsonian



Kishii

(2011)



7BL/

Lr#JS



L. racemosus



T7BL/7Lr#3S

(Lr#J)



Homoeologous

Robertsonian



Kishii

(2011)



6BL/

Lr#KS



L. racemosus



T6BL/6Lr#2S

(Lr#K)



Homoeologous

Robertsonian



Kishii

(2011)



2BL/

Lr#LS



L. racemosus



T2BL/2Lr#3S

(Lr#L)



Homoeologous

Robertsonian



Kishii

(2011)



3BL/

Lr#NS



L. racemosus



T3BL/3Lr#4S

(Lr#N)



Homoeologous

Robertsonian



Kishii

(2011)



3BS/

Lr#NL



L. racemosus



T3BS/3Lr#4L

(Lr#N)



Homoeologous

Robertsonian



Kishii

(2011)



7BL/

Lr#NS



L. racemosus



T7BL/3Lr#4S

(Lr#N)



Nonhomoeologous Kishii

Robertsonian

(2011)



234



A. Mujeeb-Kazi et al.



producing translocations involves the production of intergeneric combinations, deriving their amphiploid or backcrossing the F1 to get the BCF1, and

then advancing the amphiploid or BCF1 by further backcrossing and cytology which leads to the production of alien disomic chromosome addition

lines (2n ¼ 6x ¼ 42 þ 2 ¼ 44). If the alien source is a diploid there are seven

additional lines possible to complete the full homoeologous set. Around

each addition line exchanges in the respective homoeologous group requires

the manipulation of the Ph locus for promoting the alien and wheat partners

to recombine and thus yield translocation events across the corresponding A,

B, and D genome partner chromosomes. Targeted exchanges into a specific

chromosome are also possible and the ideal event into A, B, or D designed by

first substituting the alien chromosome for each of its partner A, B, and

D chromosome and studying the performance of the three substitutions.

The one that is most superior as to its practical performance then could

be subjected for generating exchanges—that is, alien for the A or the

B or the D. If the addition line is for group 1, then the chromosome 1 alien

could be recombined with 1A or 1B or 1D by suppressing the Ph activity as

classically demonstrated by Riley et al. (1968).

Relatively new has been the use of the ph1b genetic stock (Sears and

Sears, 1978) to obtain translocations. The strategy has been reported for

manipulating wheat amphiploids (2n ¼ 8x ¼ 56; AABBDDEbEb) with the

PhPh status in inducing multiple wheat/alien translocations (MujeebKazi, 2003) and deriving compensating translocation euploids in a wheat/

Th. bessarabicum combination targeted for salt tolerance (Kazi, 2011). This

appears to be an effective strategy when the trait inheritance is polygenic

and preferred for tolerance to heat, drought, and salinity. When a disomic

addition is identified as being trait positive, then that particular addition line

could be targeted as shown in Fig. 4.16 for a hypothetical chromosome IEb

recombined with 1A or 1B or 1D. The homoeologous translocation vary

from having the alien portion associated with either wheat chromosome

arm (reduced chromatin) or being attached to wheat long or short arm at

the centromere and called “Robertsonian.” In general that smaller the alien

chromatin, the more effective would be the translocation for wheat

improvement. Both forms have been obtained by Kazi (2011) when instead

of alien addition lines the amphiploid was involved in the production

of translocations.

The example described that has exploited Th. bessarabicum has just

scratched the surface of what lies ahead as numerous amphiploids and partial

amphiploids exist in the global wheat germplasm holdings that can be utilized



Genetic Diversity for Wheat Improvement as a Conduit to Food Security



235



Figure 4.16 A backcross 1 derivative from Triticum aestivum/Thinopyrum bessarabicum//

T. aestivum with 50 chromosomes with 6 complete Th. bessarabicum chromosomes, one

that is a Robertsonian translocation and one having a terminal alien exchange.



Figure 4.17 A backcross 1 derivative from Triticum aestivum/Thinopyrum bessarabicum//

T. aestivum with 47 chromosomes with 2 chromosomes having terminal alien

exchanges.



for the production of new translocations. Around the phib base, the induction

progress gets initiated and with integral cytogenetic validation delivers an end

product homozygous translocation stocks with the Ph1bPh1b restoration in

place. These steps are demonstrated in Figs. 4.17–4.20. In Fig. 4.17 is seen

a backcross 1 derivative with 50 chromosomes where 6 chromosomes are

of the alien species, one is a Robertsonian translocation and another showing

a terminal alien segment. The background has the ph1b recessive homozygous

system. Other backcross-selfed materials provide similar exchange results as in

Fig. 4.18, where of the 47 chromosomes three are complete alien of Eb



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Th. ponticum Partial Amphiploid OK7211542

Tải bản đầy đủ ngay(0 tr)

×